This invention relates to electro-optical devices whose electromagnetic radiation absorption characteristics can be selectively altered by influence of a suitably controlled electric field. More particularly, this invention is directed to a sandwich type cell in which a layer of electrochromic material is separated by a solid, porous insulating layer from a porous counter-electrode, wherein the insulating layer is wetted with an acid electrolyte.
In U.S. Pat. Nos. 3,521,941, 3,578,843, 3,704,057 and 3,708,220, there are described electro-optical devices exhibiting a phenomenon known as persistent electrochromism wherein electromagnetic radiation absorption characteristic of a persistent electrochromic material is altered under the influence of an electric field. Such devices were employed in sandwich arrangement between two electrodes. Coloration was induced by charging the electrochromic film negative with respect to the counter-electrode, employing an external potential. The counter-electrode can be the same as the persistent electrochromic material or different.
By reversing the original polarity of the field or by applying a new field, it was also possible to cancel, erase or bleach the visible coloration.
These steps of color induction and erasure are defined as cycling.
Although the devices described in the prior applications are effective to change their electromagnetic radiation transmitting properties under the influence of an electric field, and have good operability, they include certain inherent deficiencies which tend to reduce their long-term cycle life and limit their switching speed.
It is therefore an object of this invention to provide an electrochromic light modulating device which has a faster switching speed.
A further object is to provide an electrochromic light modulating device with extended cycle life.
These and other objects of the invention will become apparent as the description thereof proceeds.